A film to be wound into a roll when used has conventionally been made of modified cellulose. In particular, cellulose triacetate (TAC) has been used for a film for movie because of its high clearness. A film has to have tensile strength greater than a certain strength because if a film has tensile strength smaller than the certain strength, the film is easily torn and thus it is necessary to join pieces of the torn film with each other. In general, a film has to have thickness thicker than 100 micrometers in order to have a tensile strength greater than the aforementioned certain strength.
However, a film having a thickness greater than 100 micrometers is bulky. Consequently a thin film made of high tensile strength polyester has been used these days in order to reduce bulk of a film while maintaining tensile strength greater than the certain limit.
However, there arises a new problem with use of a film made of high tensile strength polyester. Such a film is not easily torn even if high tensile force is applied to the film due to occurrences of film feeding jam. If the film is torn, a high load does effect the a machine for feeding the film. 0n the other hand, if high tensile strength film which is not easily torn is used, the film feeding machine may receive high load through the film when a film feeding jam occurs. This high load may cause a roller shaft of a developing device to deform. Alternatively the high load may act on a film itself to cause the film to be distorted over feet. In a latter case, it is necessary to remove distorted portions of the film and then join the remainder of the film. This work loses the advantages of use of a high tensile strength film.